Laser systems have become essential for ophthalmic surgery. They have been employed in corneal procedures for some time now with high precision and therefore considerable success. In very recent times applications for other ophthalmic procedures have been contemplated, including cataract procedures.
Lasers can be used for forming high precision cuts. These cuts are created by focusing or directing a rapid sequence of laser pulses to a scan-pattern or point-pattern. The points of the scan-pattern often form a line or layer and the laser pulses are directed to these points by a scanning system that includes deflection devices, mirrors and lenses whose alignment can be changed very quickly. In typical laser systems the pulses can have a duration or pulse length in the nanosecond, picosecond, or even femtosecond range. The pulse repetition rate can be in the kHz to hundreds of kHz range.
The power or energy of the laser pulses can be chosen to exceed a so-called photodisruption threshold. Laser pulses with a power above this threshold can disrupt the ophthalmic tissue at the target points, inducing the formation of bubbles. Lines or layers of these bubbles can weaken the mechanical connection between the tissue-portions on the opposite sides of the bubbles. Often the weakening is substantial, effectively cutting the tissue. Therefore, a subsequent manual procedure can completely separate the tissue portions with ease.
One ophthalmic procedure which could benefit from using such a high precision laser cutting system is cataract surgery. A typical cataract surgery involves a capsulotomy step and a lysis or lens fragmentation step. During lysis, energy is applied to a lens nucleus to liquefy it. During lens fragmentation, or phaco-fragmentation, the nucleus of the lens can be cut into several pieces by scanning the laser along cutting surfaces to enable the subsequent piece-by-piece removal of the nucleus. The capsulotomy involves forming a circular cut on the anterior portion of the capsular bag of the lens to allow the surgeon to access and remove the cut-up pieces of the nucleus.
To optimize surgical laser systems for these complex ophthalmic procedures is a great challenge. However, the optimization promises great returns in terms of the precision and efficacy of the surgical procedures.